“PROTECTION FROM CORROSION BY ORGANIC COATING”

8/3/2019 PROTECTION FROM CORROSION BY ORGANIC COATING

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PROTECTIONFROMCORROSION BYORGANIC

COATING

SUBMITTED TO: MS. KULJEET

KAUR

SUBMITTED BY:

AMARDEEP TIRKEY

REG. NO.:10802977

ROLL NO.:R190B54

SECTION: B

COURSE CODE: 104

COURSE: DIPLOMA + B.TECH

INTEGRATED [M.E.]

YEAR/SEMESTER: 2ND / 3RD


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PROTECTION FROM CORROSIONBY ORGANIC COATING

INTRODUCTION

The corrosion is a phenomenon which is widely observedwith almost all metals. The most common and convenientmethod of protecting a metal against corrosion is by a

coating, especially an organic coating. The main function ofan organic coating is to serve as a protective barrier againstcorrosion besides having an aesthetic appeal.

DFINITION

Organic coating are inert organic barriers like paint

varnishes, lacquers and enamels. Plied on metallic surfacesand other constructional materials for both corrosionprotection and decoration.

The protection value of such coating depends on:

1. Its chemical inertness to the corrosive environment2. Its good surface addition.3. Its impermeability to water, salts and gases

4. Its proper application method.

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PAINTS

Paint is a mechanical dispersionmixture of one or more pigments in avehicle, the vehicle is a liquidconsisting of non volatile film formingmaterial drawing oil and highlyvolatile solvent, thinner .When a paintis applied to a metal surface usuallyby brushing or spraying, the thinnerevaporates while the drawing of oil

slowly oxidized forming a drypigmented film.

Paint is used to protect, preserve anddecorate (such as adding color), or add functionality to anobject or surface by covering it with a pigmented coating. Anexample of protection is to retard corrosion of metal. Anexample of decoration is to add festive trim to a room'sinterior. An example of added functionality is to modify light

reflection or heat radiation of a surface. Another example offunctionality is the use of color to identify hazards or toidentify the function of equipment, such as pipelines ormilitary ammunition.

Paint can be applied to almost any kind of object. It is used,among many other uses, in the production of art, inindustrial coating, as a driving aid (road surface marking), oras a barrier to prevent corrosion or water damage. Paint is a

semi finished product, or intermediate good as the finalproduct is the painted article itself.

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CHARACTERISTICS OF GOOD PAINT

It should b fluid enough to be spread easily over theprotected surface

It should possess high covering power It should form a quiet tough uniform adherent and

impervious film

Its film should not get cracked on drawing It should protect the painted surface from corrosion

effects of environment It should form film, the colour of which is quiet stable to

the effect of atmosphere and other agencies

Its film should be glossy

Its film should be stable It can be prepared in such a consistency as to be easily

applicable with brush or spraying device and that ityields a smooth and uniform surface.

It should possess high addition capacity to the materialover which it is intended to be used

CONSTITUENTS OF PAINT

PIGMENT

It is a solid substance which Is an essential constituent ofpaint. Its functions are to:

provide capacity to paint

provide strength to the paint

provide desired colour to thepaint give aesthetical appeal i.e.

pleasing to look at to the paintfilm

give protection to the paint filmby reflecting harmful ultravioletlight

provide resistance to the paint

against abrasion/wear

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improve the impermeability of paint film to moisture

increase weather resistance of the film

Pigment used as whites (such as white lead, zinc oxide,lithophone, titanium oxide) or coloured:

Red - red lead, ferric oxide, venetian chrome red Green - chromium oxide Blue - Persian blue Black-carbon black Brown-brown umber etc.

CHARACTERISTICS OF GOOD PIGMENT

Opaque Chemically inert so that paint film has stability and

longer life. Non toxic so that there is no bad effect on the health of

painter as well as inhabitants

Freely mixable with film forming constituents, oil Cheap

VEHICLE OR DRYING OIL

It is a film forming constituent of paint, these are glycerylesters or high molecular fatty acids generally present in

animal and vegetable oils.

CH2COOR

CHCOOR

CH2COOR

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FUNCTIONS OF DRYING OIL

Main film forming constituents Vehicle or medium Toughness

Adhesions Durability Water proofness

FATTY ACID PRESENT IN OIL AND FATS

NAME OF THE ACID FORMULA POSITION OF THEUNSATURATION

Caproic C5H11COOH Saturated

Caprylic C7H15COOH SaturatedCpric C9H19COOH Saturated

Lauric C11H23COOH Saturated

Myristic C13H27COOH Saturated

Palmitic C15H31COOH Saturated

Stearic C17H35COOH Saturated

Archidic C19H39COOH Saturated

Behenic C21H43COOH Saturated

Lingoceric C23H47COOH Saturated

Cerotic C25H51COOH Saturated

Oleic C17H33COOH Unaturated

Linoleic C17H31COOH Unaturated

Linoenic C17H29COOH Unaturated

Eleostearic C17H29COOH Unaturated

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REACTION IN DRYING OILS

The oil film after it has been applied on the protectedsurface, absorbs oxygen(of the air at the double bonds,forming peroxides, diperoxide and hydro peroxide whichisomerise ,polymerize and condense to form a characteristictough, coherent, hard, elastic, insoluble, infusible, highlycross linked structure macro molecular film. The finalhardened product actually resembles thermosetting resin inchemical structure.

DRYING OF PAINT FILM

THINNER

Reduce the viscosity of the paint to suitable consistency sothat it can easily handled and applied:

dissolve vehicle and the additives in thevehicle

suspend the pigments increase the penetrating power of the

vehicle

increase the elasticity of the paint film help the drawing of paint film as they evaporate

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Common thinners used are turpentine(produced by thedistillation of resinous exudation of some kind of pinetrees),minerals spirits(frompetroleum)benzene,dipentene,naphtha,toluol,xyrol,carosene

,methylatd naphthalene etc.

DRIERS

Driers are oxygen carrier catalystthey accelerate thedrawing of oil film through oxidation, polymerization andcondensation. Thus there main function is to improve thedrawing quality of the oil film.

The most effective driers are resonates,linoleates, tungstates and naphthenatesof Co, Mn, Pb and Zn.

Cobalt substances are the mostefficient of all and are surface drier.

Lead substances are bottom driers. Manganese substances are thorough driers.

EXTENDERS OR FILLERS

They are low refractive indices material generally of whitecolour added to

reduce the cost increase durability of the paint

provide negligible covering power of the paint

help to reduce the cracking of dry paint film andsometimes help to keep the pigments in suspension

surf to fill voids in the film

increase random arrangement of the pigment particles

act as carriers of the pigment colour

Important extenders used are barites (BaSo4) talc, asbestos,ground silica, gypsum, ground mica, slate powder, chinaclay, whiting (CaCo3), magnesium silicate, diatomite clay,

calcium sulphate etc.

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PLASTICIZERS

Sometimes plasticizers are incorporated in the paint:

To provide elasticity to the film

To minimize the cracking

Common plasticizers used are tricresyl phosphate, triphynylphosphate, tributyl phthalate, diamyl phthalate and dibutyltartarate.

ANTISKINNING OF OILS

They are sometimes added to some paints with the object topreventing gelling and skinning of the paint.

Important antiskinning agents are polyhydroxyl phenols.

FORMULATION OF THE PAINTS

Manufacture of paints depends upon composition of paint to

meet specific requirements. These requirements are:

Hiding power

Colour fastness

Weather resistance

Consistency

The requirements are met by proper choice of pigments,vehicles, and extenders by paint formulator. The most

important concept for modern paint formulator is:

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PIGMENT VOLUME CONCENTRATION [P.V.C.]:

PVC is the concentration by volume of the pigmentsexpressed as a percentage of the total volume of non-

volatile constituents of the paints.

It is mathematically expressed as:

P.V.C. = Volume of the pigment in paint

____________________________________________________

Total volume of non volatile constituents ofthe paint

IMPORTENCE OF P.V.C.:

The P.V.C. largely controls such factor as gloss, washability,adhesion and durability. Thus:

When the P.V.C. is increased, the gloss decreases, untilpaint becomes flat.

With the increase in P.V.C., the relative quantity ofbinder decreases, therefore, film formed loses cohesionand hence durability. So, with the increase in P.V.C.,the adhesion and durability of the paint-film decreases.

With the increase in P.V.C., the washability of paint filmdecreases. Extenders when added to a paint, amount to increases

in P.V.C., and thus, decreases washability, durabilityand adhesion. So, in case of the pigment is costly andits covering power is high a portion of the pigmentmassy economically be replaced by extenders, withoutsacrificing the covering power of the pigment.

Opacity of the white paint is created by the difference

in the refractive indices of the pigment and vehicle. It is

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also influenced by the size of the dispersed pigmentparticles and P.V.C.

FAILURE OF THE PAINT FILM:

Paint is considered to be failed in the following cases:

1. CHALKING :

It is the progressive powdering of the paint film onthe painted surfaces. This occurs due to improperdispersion of pigment in vehicle or destruction ofbinder by continuous exposure of light.

2. FLAKING :

It is the peeling of the paint film on the paintedsurface. This is due to the presence of dustparticles or greasy matters in the paint. Theseforeign matters result in poor adhesion of thepaint.

3. CRACKING :

Cracking of the paint film is due to the unequalexpansion or contraction of different coats of thepaint, caused by variation of the temperature ofthe exposed film.

4. COLOUR CHANGE OF THE PAINT FILM

Colour change of the paint film after some time isdue to the chemical effect of atmospheric gases

on the paint.

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PREVENTION:

Scientific mixing and proportioning of the ingredients ofproper characteristics.

Using only suitable and selected paint for particularjob.

Preparing carefully the surface, before application ofthe paint.

Applying a suitable primer coat. Properly applying the paint evenly Allowing each paint coat to dry sufficiently, before the

newer or next coat is applied.

VARNISHES

Varnish is a homogeneous colloidal dispersion solution ofnatural or synthetic resin in oil or thinner or both. It is usedas protective and or decorative coating of suitable surfaces

and dries by evaporation, oxidation and polymerization of itsconstituents; leaving behind a hard, transparent, glossy,lustrous and durable film. There are two main types ofvarnishes:

OIL VARNISH [OR OLEORESINOUS VARNISH]:

It is a homogenous solution of one or more natural orsynthetic resin in a drying oil and a volatile solvent. The

presence of oil reduces the natural brittleness of the pureresin film. This type of varnish dries up by the evaporation ofthe volatile solvent, followed by oxidation andpolymerization of the drying oil. Consequently suchvarnishes take comparatively longer period [about 24 hrs.]for drying, but the film produced hard, quiet lustrous anddurable. An example is copal varnish [prepared by dissolvingcopal linseed oil and mixing a quality of turpentine]. Theyare used for exterior as well as interior works.

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Drying of an Oleoresinous

SPRIT VARNISH:

It contains a resin dissolved in completely volatile solvent.

Such a varnish dries by evaporation of the solvent. Spritvarnish dries quiet rapidly, leaves behind a film which isbrittle and, so has a tendency to crack or peel off. Moreover,the film is easily affected by weathering. An example is spiritvarnish. Such varnish are used, usually, for polishing woodenfurniture.

CHARACTERISTICS OF VARNISHES:

It should be..

Be should soft and tender

Adapt itself to the contraction/ expansion of coatedmaterial like wood due to temperature variation.

Dry quickly

Produce a protective film (a hard, tough, durable and

quiet resistance to wear and tear) Produce glossy and shining film on drying

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Yield aesthetical appealing film

Yield elastic film, which does not crack or peel off ondrying

Yield film, whose colour does not fade or change on

exposure to atmosphere weather. Not shrink or crack after drying

CONSTITUENTS OF VARNISHES

I. Resin in use are:

Natural resin (like shellac, kauri, rosin, copal,dammar, manila etc.)

Synthetic resin (like phenol-aldehyde, alkyds,

urea-formaldehyde, terpene polymer etc.)

The resin, in general, are characterized by highresistance to weathering and chemical action, elasticityof film, good adhesion, high luster and in certain cases,high colour, stability to heat and light. Thus resin invarnish provides an element of hardening, resistanceto weathering, durability, resistance to chemical actionand water proofness.

II. Drying Oils

Principal oils used are linseed oil, tung oil, dehydratedcastor oil, soyabean oil, oticia oil, perilla oil, fish oiletc They dry by oxidation and polymerization.

III. Solvent or Thinners

They are usually employed are turpentine, petroleum

spirits , coal-tar-nephtha, kerosene, xylol, tolyl, butyland ethayl alcohol, amyl acetate acetone etc

IV. Driers

They are added to enhance the drying rate of oilconstituents. These include Pb, Co and Mn linoleatesnephthanates resonates etc.

V. Antiskinnig Agent

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It is like tert- amyl phenol, guiacol, etc..

Uses:

for the protection of the articles against corrosion as a brightening coat to a painted surface

For improving the appearance and intensifyingthe ornamental grains of wood surfaces.

ENAMELS

Enamel paint is a paint that air dries to ahard, usually glossy, finish. In reality,most commercially-available enamelpaints are significantly softer than eithervitreous enamel or stoved synthetic

resins.With respect to paints enamel is afanciful term, implying that an ordinarylatex or oil-based paint has the sameproperties as true, fired vitreous enamel.Some enamel paints have been made by adding varnish tooil-based paint. The term sometimes refers to oil-modifiedpolyesters that were introduced in the early 1930s. The oil isrequired to stop or enhance the cross linking of the paint inorder to achieve sufficient flexibility of the paint film.

Typically the term "enamel paint" is used to describe oil-based covering products, usually with a significant amount

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of gloss in them, however recently many latex or water-based paints have adopted the term as well. The term todaymeans "hard surfaced paint" and usually is in reference topaint brands of higher quality, floor coatings of a high gloss

finish, or spray paints.

USES

Guitars - may be used as a DIY solution to dead andscurfy guitar.

Floor enamel - May be used for concrete, stairs,basements, porches, and patios.

Fast dry enamel - Can dry within 10-15 minutes ofapplication. Ideal for refrigerators, counters, and otherindustrial finishes.

High-temp enamel - May be used for engines, brakes,exhaust, and BBQs.

Enamel is also used on wood to make it resistant to theelements via the waterproofing & rot proofing

properties of enamel. Generally, treated surfaces lastmuch longer and are much more resistant to wear thanuntreated surfaces.

Nail-enamel - Used to polish the nails

LACQUERS

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In a general sense, lacquer is a clear or coloured varnishthat dries by solvent evaporation and often a curing processas well that produces a hard, durable finish, in any sheenlevel from ultra matte to high gloss and that can be furtherpolished as required.

The term lacquer originates from the Portuguese word forlac, a type of resin excreted from certain insects.Regardless, in modern usage, lac-based varnishes arereferred to as shellac, while lacquer refers to other polymersdissolved in Volatile Organic Compounds (VOCs), such asnitrocellulose and later acrylic compounds dissolved in asolvent generally referred to as lacquer thinner. While bothlacquer and shellac are traditional finishes, lacquer is moredurable than shellac.

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EMULSION PAINTS

An 'emulsion' [IPA]: is a mixture of twoimmiscible (unbendable) liquids. One

liquid (the dispersed phase) is dispersedin the other (the continuous phase).Many emulsions are oil/water emulsions,with dietary fats being one commontype of oil encountered in everyday life.Examples of emulsions include butterand margarine, milk and cream, andvinaigrettes; the photo-sensitive side ofphotographic film, magmas and cutting

fluid for metal working. In butter andmargarine, fat surrounds droplets ofwater (a water-in-oil emulsion). In milkand cream, water surrounds droplets offat (an oil-in-water emulsion). In certaintypes of magma, globules of liquid NiFemay be dispersed within a continuousphase of liquid silicates. Emulsification isthe process by which emulsions are

prepared.

Emulsion is also a term used in the oilfield as untreated well production thatconsists primarily of crude oil and water.[citation needed]

Emulsions tend to have a cloudy appearance, because themany phase interfaces (the boundary between the phases is

called the interface) scatter light that passes through theemulsion. Emulsions are unstable and thus do not formspontaneously. Energy input through shaking, stirring,homogenizing, or spray processes are needed to form anemulsion. Over time, emulsions tend to revert to the stablestate of the phases comprising the emulsion. Surface activesubstances (surfactants) can increase the kinetic stability ofemulsions greatly so that, once formed, the emulsion doesnot change significantly over years of storage. Vinaigrette is

an example of an unstable emulsion that will quicklyseparate unless shaken continuously. This phenomenon is

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called coalescence, and happens when small dropletsrecombine to form bigger ones. Emulsions can also sufferfrom creaming, the migration of one of the substances to thetop of the emulsion under the influence of buoyancy or

centripetal force when a centrifuge is used.

Emulsions are part of a more general class of two-phasesystems of matter called colloids. Although the terms colloidand emulsion are sometimes used interchangeably,emulsion tends to imply that both the dispersed and thecontinuous phase are liquid.

There are three types of emulsion instability: flocculation,where the particles form clumps; creaming, where theparticles concentrate towards the surface (or bottom,depending on the relative density of the two phases) of themixture while staying separated; and breaking andcoalescence where the particles coalesce and form a layer ofliquid.

Whether an emulsion turns into a water-in-oil emulsion or anoil-in-water emulsion depends on the volume fraction of bothphases and on the type of emulsifier. Generally, the Bancroft

rule applies: emulsifiers and emulsifying particles tend topromote dispersion of the phase in which they do notdissolve very well; for example, proteins dissolve better inwater than in oil and so tend to form oil-in-water emulsions(that is they promote the dispersion of oil dropletsthroughout a continuous phase of water).

The basic colour of emulsions is white. If the emulsion isdilute, the Tyndall effect will scatter the light and distort the

colour to blue; if it is concentrated, the colour will bedistorted towards yellow. This phenomenon is easilyobservable on comparing skimmed milk (with no or little fat)to cream (high concentration of milk fat). Micro emulsionsand nano emulsions tend to appear clear due to the smallsize of the disperse phase.

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“PROTECTION FROM CORROSION BY ORGANIC COATING”

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